Guarded position selector switch with stop position means

ABSTRACT

A rotary circuit selector switch is provided with a limited range of unguarded switch positions by fixing a radially extending abutment to the operating shaft for the switch and fixing peripherally spaced axially extending stops to a stationary frame for the switch. The range of unguarded switch positions is determined by the space between the stops in which the abutment is free to reciprocate. A guarded switch position is provided by giving the shaft freedom for limited axial movement against an opposing spring and by shortening the axial length of one of the stops so as to permit the abutment to pass the shortened stop when the shaft has been moved axially against the opposing spring. The guarded switch position is so named because a deliberate effort on the part of the switch operator is required to reach the guarded position.

United States Patent [72] Inventors Raymond W. Ludlum Blanchester; David F. Warner, Brookville, Ohio [21] Appl. No. 792,384 [22] Filed Jan.21, 1969 [45] Patented Feb.2,l97l [73] Assignee Ledex, Inc.

Dayton, Ohio a corporation of Ohio [54] GUARDED POSITION SELECTOR SWITCH WITH STOP POSITION MEANS 7 Claims, 3 Drawing Figs.

[52] U.S.Cl 200/11, 200/166, 74/527 [51] Int. Cl I-I0lh 3/52 [50] Field ofSearch 200/11, 14, 166; 74/527 [56] References Cited UNITED STATES PATENTS 2,857,782 10/1958 Glueckstein et a1. 74/527 2,576,836 11/1951 Hilsinger,Jr. ZOO/14X Primary Examiner-H. 0. Jones Assistant Examiner-J. R. Scott Attorney- Dybvig & Dybvig ABSTRACT: A rotary circuit selector switch is provided with a limited range of unguarded switch positions by fixing a radially extending abutment to the operating shaft for the switch and fixing peripherally spaced axially extending stops to a stationary frame for the switch. The range of unguarded switch positions is determined by the space between the stops in which the abutment is free to reciprocate. A guarded switch position is provided by giving the shaft freedom for limited axial movement against an opposing spring and by shortening the axial length of one of the stops so as to permit the abutment to pass the shortened stop when the shaft has been moved axially against the opposing spring. The guarded switch position is so named because a deliberate effort on the part of the switch operator is required to reach the guarded position.

GUARDED POSITION SELECTOR SWITCH WITH STOP POSITION MEANS This invention relates to a guarded position switch and, more particularly, to a rotary circuit selector switch rotatable through plural unguarded switch positions and requiring an axial motion for entry into a guarded switch position.

An object of the present invention is to provide an improved rotary selector switch.

Another object of the present invention is to provide improved means to limit the positions available to a rotary selector switch.

Still another object of the present invention is to provide a rotary selector switch having a guarded position which can be reached only by deliberate action on the part of the operator.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

In the drawing, FIG. I is a section view in side elevation illustrating a rotary selector switch embodying the present invention, said section being taken substantially through the axis of the operating shaft of the switch and having portions of a control knob broken away.

FIG. 2 is an exploded perspective view of the switch illustrated in FIG. 1.

FIG. 3 is a fragmentary side elevation view illustrating a first operating condition of the switch with solid lines and illustrating a second operating condition of the switch with broken lines.

Referring to the drawing in greater detail, the switch depicted therein comprises a rotary assembly 11 which includes a shaft 12. The shaft 12 has first and second cylindrical sections 14 and 16, respectively, separated by an annular groove 18 and has an end section 20 which is of double D cross section. The double D cross section results from the removal of metal from diametrically opposite sides of an initially cylindrical portion of the shaft 12 so as to produce diametrically opposite flat surfaces on the shaft. This removal of metal creates radially disposed walls 22 on diametrically opposite sides of the shaft which are perpendicular to its flat surfaces.

The shaft 12 is journaled in a frame 10 which includes a bushing 24. The bushing 24 has a threaded portion 26 of reduced outside diameter at one end thereof and a sleeve portion 28 of reduced outside diameter at the opposite end thereof. The sleeve portion 28 is initially cylindrical, as shown in FIG. 2, and, as will be described, is swaged to reach the shape illustrated in FIG. 1. The bushing 24 has a central aperture sized to slidably receive the shaft 12. The overall length of the bushing 24 is such as to provide bearing support for maintaining the shaft 12 coaxial with a rotary axis concentric to the aperture 25 in the bushing 24.

The removal of metal from the bushing 24 to produce the sleeve portion 28 creates an annular radially extending wall 27 encircling one end of the sleeve portion 28. Snugly received on the sleeve portion 28 and disposed in abutment with the wall 27 is an index plate 30. The index plate 30 has a central bore 32 which slidably receives the sleeve portion 28. With the plate 30 mounted on the sleeve portion 28 and in facial contact with the wall 27 of the bushing 24, the outer end of the sleeve portion 28 is staked at peripherally spaced intervals to displace metal teeth 29 outwardly so as to entrap the index plate 30 on the bushing 24.

The bushing 24, index plate 30 and parts assembled thereto, taken collectively, comprise the aforementioned frame 10 in which the shaft 12 is journaled and to which switch parts to be later described are connected.

The index plate 30 has a plurality of radially disposed ribs 34 raised from that face thereof which faces away from the wall 27 of the bushing 24. As will appear later in this description. the ribs 34 cooperate to provide stable circuit selector positions for the switch to be described.

The index plate 30 is provided with diametrically disposed apertures 36a and 36b which, as will be later described, are employed in mounting switch parts to the plate 30.

Facially contacting the swaged end of the sleeve portion 28 is an abutment plate 38 which has a double D opening 40 slidably fitting the double D section 20 of the shaft I2. The abutment plate 38 is thus nonrotatably keyed to the double D section 20.

The abutment plate 38 has a circular periphery with the exception of a radially outwardly extending abutment 42 having spaced side walls 46 and 48 extending radially from the otherwise circular periphery of the abutment plate 38. The abutment 42 bordersa circular aperture 43 sized to freely receive a ball detent 44. As best appears in FIG. 1, the aperture 43 is spaced radially from the geometric center of the opening 40 so as to support the ball detent 44 for rolling engagement with the ribs 34 on the index plate 30. As appears in FIG. I. the sleeve portion 28, after the swaging thereof, has a sufficient axial length to hold the abutment plate 38 away from rubbing contact with the ribs 34 on the index plate 30.

A circular detent spring 52 is mounted in facial contactwith the abutment plate 38. The detent spring 52 has a central double D opening 54 which slidably fits the double D shaft section 20, and thereby keys the detent spring nonrotatably to the shaft section 20. The detent spring 52 also has an arcuate opening or window 56 concentric to the opening 54 and extending more than but less than 360, about the opening 54. The window 56 separates a peripheral band 58 from the central body of the detent spring 52 so as to enable the band 58 to flex somewhat independently of the central body of the spring 52.

With the abutment plate 38 in facial contact with the swaged end of the sleeve portion 28 and with the ball detent 44 seated in the aperture 43, the detent spring 52 is slid onto the shaft section 20 to bring its central body into facial contact with the abutment plate 38. The central body of the detent spring 52 is then fixedly secured adjacent the abutment plate 38 by swaging portions of the shaft section 20 immediately adjacent the central portion of the detent spring 52 to form retaining bosses 53 shown in FIG. 1. In this fashion the abutment plate 38 and detent spring 52 become fixed parts of the aforementioned rotary assembly 11.

To assure that the ball detent 44 is properly located with respect to the peripheral band 58 during the foregoing assembly operation, the abutment plate 38 is provided with an integral cylindrical protuberance 50 which slidably enters an aperture 60 in the detent spring 52. When the protuberance 50 has been seated in the aperture 60, the ball detent 44 is automatically aligned at the center of the peripheral band 58 in the detent spring 52.

After the detent spring 52 is secured on the shaft 12, the bushing 24 is forced into facial contact with the abutment plate 38 by means of a coil spring 64 slidably received on the shaft 12 and coiled about the second cylindrical shaft section 16. The spring 64 is confined on the second cylindrical shaft section 16 by means of a split ring fastener 66 received in the groove 18 of the shaft 12. The fastener 66 is thus also a fixed part of the rotary assembly 11.

The relaxed length of the spring 64 exceeds the separation obtainable along the length of the shaft 12 between the fastener 66 and the bushing 24. Accordingly, the spring 64 cannot be placed between the fastener 66 and the bushing 24 except by a compression of the spring 64. This generates a restoring force sufficient to hold the bushing 24 in firm facial contact with the abutment plate 38. This restoring force is also sufficiently large in relation to the reaction force associated with the detent spring 52 that the ball detent 44 is caused to push the band 58 of the detent spring 52 away from the abutment plate 38 generating a force in the detent spring 52 which presses the ball detent 44 against the ribbed face of the index plate 30. The ball detent 44, detent spring 52 and index plate 30 cooperate to provide a detent assembly in which the spring loaded ball seeks stable positions between the ribs 34 and yieldingly resists rotary movements of the abutment plate 38 away from said stable positions.

The spring 64 is a helix of wire having a uniform diameter sized to closely fit the outer diameter of the shaft 12. When the shaft 12 is pushed to the left. as viewed in FIG. 1, thus further compressing the spring 64, the successive convolutions forming the spring 64 move into contact, one with the other, so as to form a rigid sleeve between the fastener 66 and the bushing 24. The formation of this rigid sleeve upon compression of the spring 64 is indicated in broken line detail in FIG. 3. When the spring 64 has compressed to a rigid sleeve, further approach of the fastener 66 toward the bushing 24 is precluded. The spring 64 cooperating with the fastener 66 thus serves to limit the extent to which the abutment plate 38 can be moved away from the bushing 24. The spring 64, accordingly, operates to establish a first axial position for the rotary assembly 11 by yieldingly biasing the rotary assembly in one direction to the limit allowed by the bosses 53 on the shaft 12, and, upon compression thereof in the opposite direction, to establish a second axial position for the rotary assembly 11 by forming a rigid sleeve between the bushing 24 and the fastener 66.

The spring 64 is sized to have a length, when compressed to its rigid sleeve condition, which permits a separation between the ribbed face of the index plate 30 and the face of the abutment plate 38 farthest therefrom substantially equal to the diameter of the ball detent 44. The length of the spring 64, when fully compressed, thus assures that the ball detent 44 will always be trapped between the index plate 30 and the abutment plate 38 by at least the thickness of the abutment plate 38. Accordingly, the spring 64 can be compressed to its fullest extent without concern that the ball detent 44 may roll outwardly from the aperture 43.

As previously mentioned, the index plate 30 has apertures 36a and 36b for the purpose of assembling switch parts thereon. Thus, an insulating wafer 74, which supports switch contacts thereon in an arrangement to be described, is mounted to the plate 30 by means of elongated struts 70a and 70b passing through the apertures 36a and 36b. The wafer 74 is spaced apart from the plate 30 by means of sleeves 72a and 72b surrounding the struts 70a and 70b. The sleeves 72a and 72b also serve to hold a stop ring 68 in facial contact with the index plate 30. Upon assembly of the stop ring 68, sleeves 72a and 72b and the wafer 74 on the struts 70a and 70b, the assembly istightly secured by means of threaded nuts 71a and 71b engaging threaded ends of the struts 70a and 70b. To minimize electrical leakage from the contacts mounted on the wafer 74 through the struts 70a and 70b to other metallic components of the switch assembly, insulating spacers 78a and 78b separate the nuts 71a and 71b from the wafer 74.

The stop ring 68, which is provided with apertures 69a and 69b to receive the struts 70a and 70b, is a stamped metal sheet having a plurality of abutment stops 80a, 80b, 80c and 80d struck upwardly therefrom. 1n the embodiment illustrated, the stop ring 68 also has a shortened stop or half-stop 82 projecting upwardly therefrom. The upstanding stops 80a-80d and 82 are spaced at angular intervals along the inner periphery of the ring 68.

The stop ring 68, which is best shown in FIG. 2, is formed by first stamping a flat sheet metal member, not shown, to provide an annular ring having a plurality of radially disposed spokes of equal length projecting inwardly from the inner periphery of the ring. The spokes are then all struck upwardly to positions perpendicular to the plane of the ring, thus forming an annular array of stops, each substantially identical to the illustrated stops 80a-80d. The ring 68, when in this condition, is not illustrated in the drawing.

When an order for switches of a given character has been received, a portion of the stops are cut away from the inner periphery of the ring 68. Thus, in the embodiment illustrated, the ring 68 initially comprised 12 stops equally distributed along the inner periphery of the ring 68. To produce the ring 68, as illustrated, seven of the 12 stops were cut away. An additional one of the 12 stops was cut in half to form the shortened stop 82.

in the assembly of FIG. 1, the stops a-80d and 82 of the stop ring 68 anddisposed a radial distance from the axis of the shaft 12 which exceeds the radius of the circular portion of the, abutment plate 38, but which is less than the outer radius of the abuunent 42. In effecting the assembly of FIG. 1, the abutment 42 is located with reference to the stop ring 68 so as to project into the open region where stops have been removed, thus being freely movable between the half-stop 82 and the full stop 80a.

The axial height of the half-stop 82, added to the thickness of the ring portion of the stop ring 68, exceeds the axial dimension of the lip 29 on the bushing 24. Accordingly, the axial dimension of the half-stop 82, as measured from the ribbed face of the index plate 30, is sufficient to block rotary movement of the abutment plate 38 as the abutment 42 is advanced toward the position occupied by the half-stop 82. Such blocking occurs when the side wall 46 of the abutment 42 engages the half-stop 82. Likewise, when the shaft 12 is rotated in the opposite direction, the side wall 48 of the abutment 42 will engage the stop 80a to limit movement of the abutment plate 38.

As will be explained more fully in the ensuing remarks, the several switch positions which can be reached by movement of the abutment 42 between the full stop 80a and the half-stop 82 comprise unguarded switch positions. These positions are reached by a relatively easy rotation of the shaft 12 accomplished manually by means of a control knob 92 fixed to the shaft 12 by a locking screw 94. The present construction allows the span of positions which can be reached by the abutment 42 to be increased by a manual depression of the control knob 92 so as to compress the spring 64 to the, previously described rigid spring condition. With the knob 92 so depressed, the abutment 42 is moved axially away from the index plate 30 a distance exceeding the height of the half-stop 82. This movement disables the guard formed by the abutment 42 and the half-stop 82, thus allowing passage of the half-stop 82 by the abutment 42 to a position where the abutment 42 will engage the next adjacent full stop 80d. The switch position thereby reached is referred to as a guarded switch position.

A representative switch device for operation by the above described switch assembly includes the previously described wafer 74 having apertures 75a and 75b to receive the struts 70a and 70b. The wafer 74 is an annular body having eight radially disposed contact members 76a, 76b, 76c, 76d, 76e, 76f, 76g and 76h mounted thereon. Centrally received within the wafer 74 is an insulating rotor insert 77 having a double D shaped aperture which fits the double D shaped shaft section 20. The shaft 12 thus has driving connection with the insert 77.

An annular conductor 93 is fastened to one face of the insert 77 in conventional manner. An annular conductor 97 is likewise fastened to the opposite face of the insert. The conductors 93 and 97 are slightly larger in outer diameter than the inner periphery of the wafer 74 and by lapping over said periphery cooperate to support the insert 77 in coplanar alignment with the wafer 74.

The conductor 93 has a radially outwardly projecting tab 96 adapted to wipe under the contact members 76a--76h on the wafer 74. The conductor 97 is continuously engaged by a feeder contact 101 mounted on the wafer 74 and is rendered electrically common to the conductor 93 and tab 96 by means of a fastener 99 formed integral with the conductor 93 which passes through the body of the wafer 74 to contact the conductor 97. Accordingly, rotary motion of the shaft 12 to pass the tab 96 under successive contact members in the group 76a76h electrically connects the feeder contact 101 to each contact member wiped by the tab 96.

By means of the apertures 75a and 75b in the wafer 74, the contact members 76a-76h are fixed at predetermined angular intervals with reference to the axis of the shaft 12. By means of the apertures 36a and 36b in the index plate 30, there is a predetermined angular relationship between the ribs 34 and the same axis. The angular relationship between the abutment 42, which cages the ball detent 44, and the tab 96 is such that each stable position for the ball detent 44 as determined by the ribs 34 locates the tab 96 under one of the contact members 76a76h on the wafer 74. The seven contact members 76a, 76b, 76c, 76d, 76e, 76f, and 76g are at unguarded positions and, accordingly, mere rotation of the knob 92 can selectively place the tab 96 in a stable position in contact with any of the seven contact members 76a, 76b, 76c, 76d, 76e, 76f and 763. As described, the tab 96 can be caused to engage the guarded contact member 76h only by axially depressing the knob 92 and rotating the knob so as to pass the abutment 42 over the half-stop 82 of the stop ring.

It will be obvious to those skilled in the art that additional I guarded positions can be provided by merely providing additional half-stops. It will also be recognized that the number and location of guarded and unguarded switch positions, as well as the angular locations of such positions, can be varied as the manufacturer desires by merely choosing which of the full stops actually remain on the stop ring 68 and which of the full stops are reduced to half-stops.

To facilitate the axial depression of the knob 92 required to reach the guarded switch position, or positions, the described switch assembly is preferably mounted to an instrument panel 89. Such panel is provided with an appropriate aperture to receive the threaded portion 26 of the bushing 24. The bushing 24 is securely fixed to the panel 89 by means of a threaded nut 91 clamping the bushing 24 against the panel 89.

From the foregoing description, it will be recognized that the present invention provides a switch assembly of generally conventional construction mountable to instrument panels in the conventional fashion, but offers the unique advantage of one or more guarded switch positions which can be reached only by a deliberate depression and rotation of the control knob for the switch.

We claim:

1. A switch device comprising, in combination: a frame, a rotary assembly journaled in said frame for rotation about a rotary axis, switch means having parts connected respectively to said rotary assembly and said frame and switchable between plural operating positions by rotation of said rotary assembly about said rotary axis, said rotary assembly including an abutment, a first stop connected to said frame, said rotary assembly movable axially relative to said frame between first and second positions, said abutment, when said rotary assembly is rotated in said first position, operative to engage said first stop thereby limiting the number of operating positions reached by said switch means when said rotary assembly is in said first position, said abutment, when said rotary assembly is rotated in said second position, operative to pass said first stop thereby adding to the number of operating positions reached by said switch means, said switch device including a second stop connected to said frame, said second stop operative when said rotary assembly is rotated in said second position to engage said abutment thereby limiting the operating positions reached by said switch means when said rotary assembly is in said second position.

2. The switch device of claim 1 wherein said first and second stops are circumferentially spaced about said rotary axis and, when said rotary assembly is in said first position, said abutment projects into the space between said first and second stops.

3. The device of claim 2 wherein said frame includes a stop ring encircling said rotary axis, said first and second stops projecting axially from said ring at locations spaced circumferentially on said ring.

4. The device of claim 3 wherein the axial projection of said second stop from said ring exceeds the axial projection of said first stop from said ring, said abutment, when said rotary assembly is in said second position, operative to pass said first stop but inoperative to pass said second stop.

5. A switch device comprising, in combination: a frame, a rotary assembly journaled in said frame for rotation about a rotary axis, switch means havin parts connected respectively to said rotary assembly and said rame and switchable between plural operating positions by rotation of said rotary assembly about said rotary axis, said rotary assembly including an abutment, a first stop connected to said frame, said rotary assembly movable axially relative to said frame between first and second positions, yielding means acting between said frame and said rotary assembly to bias said rotary assembly to said first position, said abutment, when said rotary assembly is rotated in said first position, operative to engage said first stop thereby limiting the number of operating positions reached by said switch means when said rotary assembly is in said first position, said abutment, when said rotary assembly is rotated in said second position, operative to pass said first stop thereby adding to the number of operating positions reached by said switch means, said rotary assembly including a shaft coaxial with said rotary axis, a fastener engaging said shaft. said yielding means comprising a spring coiled around said shaft and acting between said fastener and a portion of said frame to bias said shaft to said one position, said spring compressing to a substantially rigid sleeve between said fastener and said frame to terminate axial movement of said shaft at said second position.

6. A switch device comprising, in combination: a frame, a rotary assembly journaled in said frame for rotation about a rotary axis, switch means having parts connected respectively to said rotary assembly and said frame and switchable between plural operating positions by rotation of said rotary assembly about said rotary axis, said rotary assembly including an abutment, a first stop mounted on said frame, said rotary assembly movable axially relative to said frame between first and second positions, said abutment, when said rotary assembly is rotated in said first position, operative to engage said first stop thereby limiting the number of operating positions reached by said switch means when said rotary assembly is in said first position, said abutment, when said rotary assembly is rotated in said second position, operative to pass said first stop thereby adding to the number of operating positions reached by said switch means, yielding means acting between said frame and said rotary assembly to bias said rotary assembly to said first position, said frame including an index plate, said rotary assembly caging a detent, said detent movable axially relative to said rotary assembly, said switch device including a detent spring acting between said rotary assembly and said detent to bias said detent axially against said index plate, the reaction of said detent spring against said rotary assembly opposing the bias of said yielding means, the bias of said yielding means on said rotary assembly exceeding the reaction of said detent spring against said rotary assembly.

7. The switch device of claim 6 wherein said frame includes a stop ring surrounding said rotary axis, said first stop attached to and projecting axially from said stop ring, said stop ring having an open center, said detent passing through said open center to engage said index plate. 

1. A switch device comprising, in combination: a frame, a rotary assembly journaled in said frame for rotation about a rotary axis, switch means having parts connected respectively to said rotary assembly and said frame and switchable between plural operating positions by rotation of said rotary assembly about said rotary axis, said rotary assembly including an abutment, a first stop connected to said frame, said rotary assembly movable axially relative to said frame between first and second positions, said abutment, when said rotary assembly is rotated in said first position, operative to engage said first stop thereby limiting the number of operating positions reached by said switch means when said rotary assembly is in said first position, said abutment, when said rotary assembly is rotated in said second position, operative to pass said first stop thereby adding to the number of operating positions reached by said switch means, said switch device including a second stop connected to said frame, said second stop operative when said rotary assembly is rotated in said second position to engage said abutment thereby limiting the operating positions reached by said switch means when said rotary assembly is in said second position.
 2. The switch device of claim 1 wherein said first and second stops are circumferentially spaced about said rotary axis and, when said rotary assembly is in said first position, said abutment projects into the space between said first and second stops.
 3. The device of claim 2 wherein said frame includes a stop ring encircling said rotary axis, said first and second stops projecting axially from said ring at locations spaced circumferentially on said ring.
 4. The device of claim 3 wherein the axial projection of said second stop from said ring exceeds the axial projection of said first stop from said ring, said abutment, when said rotary assembly is in said second position, operative to pass said first stop but inoperative to pass said second stop.
 5. A switch device comprising, in combination: a frame, a rotary assembly journaled in said frame for rotation about a rotary axis, switch means having parts connected respectively to said rotary assembly and said frame and switchable between plural operating positions by rotation of said rotary assembly about said rotary axis, said rotary assembly including an abutment, a first stop connected to said frame, said rotary assembly movable axially relative to said frame between first and second positions, yielding means acting between said frame and said rotary assembly to bias said rotary assembly to said first position, said abutment, when said rotary assembly is rotated in said first position, operative to engage said first stop thereby limiting the number of operating positions reached by said switch means when said rotary assembly is in said first position, said abutment, when said rotary assembly is rotated in said second position, operative to pass said first stop thereby adding to the number of operating positions reached by said switch means, said rotary assembly including a shaft coaxial with said rotary axis, a fastener enGaging said shaft, said yielding means comprising a spring coiled around said shaft and acting between said fastener and a portion of said frame to bias said shaft to said one position, said spring compressing to a substantially rigid sleeve between said fastener and said frame to terminate axial movement of said shaft at said second position.
 6. A switch device comprising, in combination: a frame, a rotary assembly journaled in said frame for rotation about a rotary axis, switch means having parts connected respectively to said rotary assembly and said frame and switchable between plural operating positions by rotation of said rotary assembly about said rotary axis, said rotary assembly including an abutment, a first stop mounted on said frame, said rotary assembly movable axially relative to said frame between first and second positions, said abutment, when said rotary assembly is rotated in said first position, operative to engage said first stop thereby limiting the number of operating positions reached by said switch means when said rotary assembly is in said first position, said abutment, when said rotary assembly is rotated in said second position, operative to pass said first stop thereby adding to the number of operating positions reached by said switch means, yielding means acting between said frame and said rotary assembly to bias said rotary assembly to said first position, said frame including an index plate, said rotary assembly caging a detent, said detent movable axially relative to said rotary assembly, said switch device including a detent spring acting between said rotary assembly and said detent to bias said detent axially against said index plate, the reaction of said detent spring against said rotary assembly opposing the bias of said yielding means, the bias of said yielding means on said rotary assembly exceeding the reaction of said detent spring against said rotary assembly.
 7. The switch device of claim 6 wherein said frame includes a stop ring surrounding said rotary axis, said first stop attached to and projecting axially from said stop ring, said stop ring having an open center, said detent passing through said open center to engage said index plate. 